1. Field of the Invention
The present invention relates to a cold-cathode tube driving circuit, more particularly, to a driving circuit for driving a plurality of substantially-C-shaped cold-cathode tubes.
2. Description of the Related Art
JP-A-8-45675 describes a discharge lamp lighting apparatus of current feedback type having a switching circuit which causes the entirety or a portion of an electric current flowing through one or a plurality of discharge lamps to flow into an impedance device to thus change the impedance of the impedance device in accordance with the number of lighting circuits. According to the discharge lamp lighting apparatus, a tube current flowing through a single discharge lamp can be automatically maintained constant even when the number of discharge lamps or lighting circuits is arbitrarily changed within a preset range. Lighting of the discharge lamp is less susceptible to the influence of stray capacitance.
In JP-A-59-201398, an oscillation transformer having two secondary coils wound around a single iron core is used to light two discharge lamps connected in parallel, and is connected such that a d.c. current flows into the secondary coils in opposite directions, and first and second inductance coils are connected in opposite polarities. In the discharge lamp lighting apparatus, when one discharge lamp (the first discharge lamp) is first lighted, the current flows into the first inductance coil, whereby an induced voltage develops in the secondary inductance coil wound in opposite polarity. A high voltage is applied to the second discharge lamp by means of the induced voltage, to thus light the second discharge lamp without fail. Specifically, even when one discharge lamp has been lighted first, the voltage of the secondary coil used for supplying a voltage to another discharge lamp is prevented from dropping to the lamp voltage, thereby preventing failure to light a discharge lamp which is to be lighted later.